Re: Using "=" vs ":="

*To*: mathgroup at smc.vnet.net*Subject*: [mg70706] Re: Using "=" vs ":="*From*: "dimitris" <dimmechan at yahoo.com>*Date*: Mon, 23 Oct 2006 05:45:08 -0400 (EDT)*References*: <ehf1ks$5ds$1@smc.vnet.net>

Copy and Paste the following command in a Mathematica Notebook and then press Shift+Enter to execute it FrontEndExecute[FrontEnd`HelpBrowserLookup["MainBook", "2.5.8"]] Regards Dimitris misha wrote: > I'm going through Mathematic by Example, 2nd ed., (Abell and Braselton), > and have come across something that puzzles me. > > Chapter 2, Section 2, Example 8 > Define f(x,y)=1-sin(x^2+y^2) > > So I first try, > In[1]:= f[x_, y_]:=1-Sin(x^2+y^2) > No problem so far... > Then, > In[2]:= f[x,y] > Out[2]:=1-Sin(x^2+y^2) > Still no problem... > Then, > In[3]:=f[1,2] > Out[3]:=1-5 Sin > > Huh? > > I noticed that rather than using ":=" to "simply define" this function, > as opposed to (just) "=" to "define and compute" this function, I get > different subsequent behavior. Specifically, doing the above with just > "=", works fine. > In[1]:= f[x_, y_]=1-Sin(x^2+y^2) > .... > In[3]:=f[1,2] > Out[3]:=1-Sin[5] > > My question is, Why? What's the difference between ":=" and "=" for > defining functions? > > Thanks! > Misha